This data set is a digital elevation model (DEM) product that populates
the GLOBAL Terrain product catalog. The DEM products are generated
using the Intermap STAR-3i airborne interferometric synthetic aperture
radar (SAR) system mounted in a LearJet 36A aircraft.

The GLOBAL Terrain Digital Surface Model (DSM) data files are digital
representations of cartographic information in a grid form. DSMs consist
of a sampled array of elevations for a number of ground positions at
regularly spaced intervals. These digital data files are produced by
Intermap Technologies Inc.(Intermap) as part of the GLOBAL Terrain product
line and are licensed in 7.5-minute tiles for areas located between 0 and
56 degrees North/South. Data for locations above 56 degrees North/South are
licensed in 15-minute by 7.5-minute tiles.

GLOBAL Terrain DSM products represent the first reflective surface as
illuminated by the radar. Accuracy statements are based on areas of moderate
terrain. Diminished accuracies are to be expected in areas of extreme terrain
and dense vegetation.

GLOBAL Terrain DSMs are produced within four classes of vertical accuracy. GTF
DSMs have an accuracy of 0.5m Root Mean Square Error (RMSE) or better. GT1 DSMs
have an accuracy of 1.0m RMSE or better. GT2 DSMs have an accuracy of 2.0m RMSE
or better. GT3 DSMs have an accuracy of 3.0 RMSE or better. No in-scene ground
control points are required for GT2 and GT3 products provided that the DGPS
ground station is within 200 km of the data acquisition area. The GTF and GT1
products do require in-scene ground control.

The DSM data for 7.5-minute units correspond to the USGS 1:24,000 and
1:25,000 scale topographic quadrangle map series for available areas in
the United States and throughout the world. Each 7.5-minute DSM is based
on 5- by 5-meter, or 10- by 10-meter post spacing using the Universal
Transverse Mercator (UTM) projection. Each 7.5- by 7.5-minute tile
provides full coverage with overlap into adjacent tiles.

Purpose:

The purpose of this data set is to provide a source for current and
accurate digital elevation models with vertical accuracy of between 0.5
meter and 3 meters and post spacing of 5 or 10 meters.

The DSMs are used as a fundamental layer of information in Geographic
Information Systems (GIS) and Spatial Information Decision Support Systems
(DSS). A number of the priority layers of spatial information recognized
by the National Spatial Data Infrastructure may be derived from GLOBAL
Terrain DEMs, including elevation, hydrography, slope, aspect, and shoreline
delineation.

Supplemental_Information:

The STAR-3i system employs three principle technologies: X-band Horizontal
-Horizontal (HH) polarized SAR, a ring laser-based inertial measurement unit
(IMU), and Differential Global Positioning System (DGPS). STAR-3i was developed
by the Environmental Research Institute of Michigan (ERIM) under contract to
the U.S. Defense Advanced Research Projects Agency (DARPA).

The system is comprised of two X-band radar antennae that collect data
simultaneously. The set of acquired data are "interfered" by a digital
correlation process to extract terrain height data and geometrically
correct radar images. STAR-3i uses post-processed DGPS data, together with
precise inertial measurement data, to attain highly accurate positioning
control. Precise terrain height and positioning data are enhanced by
careful calibration of the baseline separating the two antennae.

The STAR-3i system accuracy has been independently validated by tests
conducted by the U.S. Army Topographic Engineering Center, the Institute
of Navigation, Stuttgart University and by NASA. A summary of test results
are accessible at <URL:http://www.globalterrain.com>.

The GLOBAL Terrain folder name describes the geographic location of a tile.
The GLOBAL Terrain file name encapsulates the GT processing level and the product
version number. A complete explanation of the GLOBAL Terrain file name can
be found in the GLOBAL Terrain Product Handbook. <URL:http://www.globalterrain.com/gt.asp#Product Handbook>.

Time_Period_of_Content:

Time_Period_Information:

Range_of_Dates/Times:

Beginning_Date: 20001005

Ending_Date: 20001005

Currentness_Reference:

The above dates refer to the time of field data acquisition and therefore reflect
ground conditions at that time.

This GLOBAL Terrain DSM data product was derived using Intermap Technologies
STAR-3i airborne interferometric SAR data acquisition system. The flying height is
30,000 feet Above Mean Ground. The primary look direction is West. The secondary
(alternate) look direction is None. Areas of missing data are interpolated using
continuous curvature spline over non-data areas. The phase unwrapper utilized is Goldstein.
Most incidences of non-data areas are due to radar shadow and layover due to steep terrain.
Radar shadow is a factor of the local topography. It is often found in mountainous regions
and the urban canyons of built-up areas. Occurances of non-data areas within a DEM are dependent
on the look direction of the radar. Significant bodies of water are assigned an elevation
which corresponds to the shoreline. Areas of null data are assigned the value -32767.

Spatial_Data_Organization_Information:

Direct_Spatial_Reference_Method: Raster

Raster_Object_Information:

Raster_Object_Type: Grid Cell

Row_Count: 2987

Column_Count: 3401

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:

Planar:

Grid_Coordinate_System:

Grid_Coordinate_System_Name: Universal Transverse Mercator

Universal_Transverse_Mercator:

UTM_Zone_Number: 6

Transverse_Mercator:

Scale_Factor_at_Central_Meridian: 0.9996

Longitude_of_Central_Meridian: 147 degrees West

Latitude_of_Projection_Origin: 0

False_Easting: 500000.0 meters

False_Northing: 0.0 meters

Planar_Coordinate_Information:

Planar_Coordinate_Encoding_Method: coordinate pair

Coordinate_Representation:

Abscissa_Resolution: 5.0

Ordinate_Resolution: 5.0

Planar_Distance_Units: Meters

Geodetic_Model:

Horizontal_Datum_Name: WGS84

Ellipsoid_Name: WGS84

Semi-major_Axis: 6378206.4

Denominator_of_Flattening_Ratio: 294.98

Vertical_Coordinate_System_Definition:

Altitude_System_Definition:

Altitude_Datum_Name: Mean Sea Level (EGM96)

Altitude_Resolution: 0.01 m

Altitude_Distance_Units: meters

Altitude_Encoding_Method: Implicit coordinate

Entity_and_Attribute_Information:

Detailed_Description:

Entity_Type:

Entity_Type_Label: 5 meter posting grid cell

Entity_Type_Definition:

The DSM is a 32 bit IEEE floating point value Big Endian organized
in a one-channel binary interleaved file (BIL) on a 7.5-minute
geographic (lat/long) grid in UTM projection. The origin of the
pixel is center center.